I am currently working on some galley-related code, and looking at the
e-TeX extensions to Knuth's paragraph-breaking penalty system. The roles
of \clubpenalties, \widowpenalties and \displaywidowpenalties are clear,
and it seems reasonable to provide a documented interface to these
primitives. On the other hand, \interlinepenalties seems to be very
difficult both to explain and to see a real case for use. Does anyone
have experience in using \interlinepenalties, and if so can then suggest
a good example where it works to solve a real-life problem.